1. Field of Invention
The present invention relates in general to mufflers and more particularly to mufflers of a type that is suitable for use with an internal combustion engine to muffle or silence exhaust noise produced by the engine.
2. Description of Related Art
Hitherto, various types of mufflers have been proposed and put into practical use particularly in the field of automotive internal combustion engines.
One of such mufflers is shown in Laid-open Japanese Patent Application (Tokkaihei) 9-125930. In FIGS. 15 and 16 of the accompanying drawings, there is shown the muffler of the Laid-open Application. FIG. 15 is a sectional view of the muffler and FIG. 16 is a sectional view taken along the line xe2x80x9cXVIxe2x80x94XVIxe2x80x9d of FIG. 15. As is seen from the drawings, the muffler comprises a semi-cylindrical outer case 301 having longitudinal ends 301a and 301b closed, and a regularly cylindrical inner case 302 installed in outer case 301 to extend longitudinally. As is seen from FIG. 15, inner case 302 has a gas inlet part xe2x80x9cINxe2x80x9d and a gas outlet part xe2x80x9cOUTxe2x80x9d at longitudinal ends. Within inner case 302, there are arranged front and rear inner sections 303 and 304 each having a cylindrical wall 302a with a plurality of small openings 303a and 304a. Between front and rear inner sections 303 and 304, there is arranged an intermediate space section 306 that comprises a partition wall 305 formed with a plurality of small openings 306a. Within an annular space defined between outer and inner cases 301 and 302, there are arranged front and rear outer sections 403 and 404 that are separated by an intermediate space section 308 that comprises a partition wall 307 formed with a plurality of small openings 308a. In operation, exhaust gas from an associated engine enters front inner section 303 through gas inlet part xe2x80x9cINxe2x80x9d. One part of gas in front inner section 303 is led to rear inner section 304 through intermediate space section 306 and discharged to open air through gas outlet part xe2x80x9cOUTxe2x80x9d, while the remaining part of gas in front inner section 303 is led into front outer section 403 through small openings 303a, into rear outer section 404 through small openings 308a, into rear inner section 304 through small openings 304a and discharged to open air through gas outlet part xe2x80x9cOUTxe2x80x9d. During such flow in the muffler, acoustic energy or noise of the exhaust gas is reduced or damped due to expansion/resonance effect possessed by the gas flow passages.
While, Laid-open Japanese Patent Applications (Tokkaihei) 7-13573 and 7-175485 show a sound insulating structure that is used as an under cover of an engine room of a motor vehicle for blocking noises of exhaust system of the engine from being emitted to open air. That is, for blocking noises of exhaust system, the sound insulting structure employs an acoustically improved mechanism.
Laid-open Japanese Patent Application (Tokkaihei) 11-132024 shows a muffler that is produced by practically employing the acoustically improved mechanism of the above-mentioned publications 7-13573 and 7-175485.
However, due to inherent construction, the above-mentioned known mufflers have failed to provide users with a satisfaction. That is, some are poor in muffling performance, some are high in cost or some are difficult to assemble.
It is therefore an object of the present invention to provide a muffler that is high in muffling performance, low in cost and easy to assemble.
According to a first aspect of the present invention, there is provided a muffler which comprises a case having opposed ends closed; a partition structure installed in the case to constitute a sound silencing path; inlet and outlet pipes incorporated with the sound silencing path; and a sound shielding wall structure installed in the case to constitute a part of the sound silencing path, wherein the sound shielding wall structure comprises first and second partition plates; a positioning structure that puts the first and second partition plates together to keep a given distance therebetween; a first group of projections defined by the first partition plate and projected toward the second partition plate, each projection of the first group having a first opening formed therethrough; and a second group of projections defined by the second partition plate and projected toward the first partition plate, each projection of the second group having a second opening formed therethrough, the projections of the second group respectively facing the projections of the first group having a given clearance kept therebetween.
According to a second aspect of the present invention, there is provided a muffler which comprises a case having opposed ends closed; at least one partition plate installed in the case to divide an interior of the same into two chambers; a sound shielding wall structure installed in one of the two chambers to divide the same into first and second sound chambers allowing the other one of the two chambers to serve as a third sound chamber; and pipe members projected into the case passing through the partition plate and the sound shielding wall structure to define in the case a sound silencing path including the first, second and third sound chambers, wherein the sound shielding wall structure comprises first and second partition plates; a positioning structure that puts the first and second partition plates together to keep a given distance therebetween; a first group of projections defined by the first partition plate and projected toward the second partition plate, each projection of the first group having a first opening formed therethrough; and a second group of projections defined by the second partition plate and projected toward the first partition plate, each projection of the second group having a second opening formed therethrough, the projections of the second group respectively facing the projections of the first group having a given clearance kept therebetween.